The goal of this proposal is to explore the importance of the MAPK pathway in regulating myeloid cell differentiation. The MAPK pathway is a signal transduction module downstream of p21 ras, which involves raf kinase activation of MAP kinase kinase (MAPKK) and MAPKK activation of MAPK. MAPK targets many signalling molecules including protein kinases, receptors, phospholipases, and transcription factors. Preliminary results obtained in this lab demonstrate that overexpression of constitutively active MAPKK mutants causes K562 cell differentiation. K562 cells are a useful tool to study cell differentiation because they are multipotent. For example, treatment with phorbol esters causes K562 cells differentiation into platelet precursor megakaryocytes. In contrast, upon treatment with erythropoietin, k562 cells become erythroid. Thus, the hypothesis that this proposal will address is that the MAPK pathway is necessary and sufficient for determining K562 cell differentiation towards a megakaryocyte or erythroid lineage. Studies will be carried out to identify the cell lineages induced by overexpression of active MAPKK and to determine whether MAPK activation is required for these events. The hypothesis that the kinetics or magnitude of MAPKK activation influences cell differentiation will be tested. And finally, mechanisms of MAPKK-induced differentiation will be explored by testing whether differentiation requires the production of an autocrine factor or occurs directly through the activation of lineage-specific transcription factors. Completion of these studies will provide important information about the mechanisms that govern cell differentiation.